Display driving apparatus for presenting same display on a plurality of scan lines

Abstract: A liquid crystal driving apparatus (20) has scan lines (G₁ to G N ), data lines (DL₁ to DL M ), switching elements (3) and pixel capacitors (4) arranged in a matrix form on a glass substrate (21). The switching elements (3) and pixel capacitors (4) are provided at the intersections of the data lines (DL₁-DL M ) and the scan lines (G₁-G N ). The data lines (DL₁-DL M ) are connected to a data shift register (9) via a driver circuit (7) and a latch circuit (8). A data transfer clock (C PH ) and data are input to the data shift register (9) from a controller (22). The controller (22) performs controls the outputting of the data transfer clock (C PH ) and the data in such a way as to write data, latched in the latch circuit (8), in n lines of pixels and to stop a data transfer operation of the shift register during an (n - 1) scan period.

Description: The present invention relates to a display driving apparatus according to the preamble of claim 1. In an active matrix display system, a non-linear active element is placed at each pixel to eliminate the interference of other signals, thereby achieving high image quality. Conventionally, a display driving apparatus, particularly, a display driving apparatus using a liquid crystal display (LCD) panel has switching elements 3 and pixel capacitors 4 arranged in a matrix form at the intersections of data lines DL 1 to DL M and scan lines G 1 to G N , laid out respectively in M columns and N rows, as shown in Fig. 3 showing the circuit structure of an active matrix LCD panel driver section (only one set of the switching element 3 and pixel capacitor 4 illustrated in Fig. 3). The individual scan lines G 1 -G N are connected to a scanning shift register 6 via a driver circuit 5 and the individual data lines DL 1 -DL M are connected to a data shift register 9 via a driver circuit 7 and a latch circuit 8. In this active matrix display system, pixel electrodes constituting the pixel capacitors 4 and the switching elements, for example, TFTs (Thin Film Transistors), connected to the pixel capacitors 4, are arranged on the inner face of one electrode substrate. The switching elements 3 are driven in a matrix form so that the pixel capacitors 4 are charged via the associated switching elements 3. The driver circuit 5 and the scanning shift register 6 constitute a gate driver 10, while the driver circuit 7, the latch circuit 8 and the data shift register 9 constitute a drain driver 11. A vertical sync signal V and a vertical clock signal C PV , which becomes a data transfer clock, are input to the shift register 6. The scanning shift register 6 sequentially outputs scan signals to the individual scan lines G 1 -G N via the driver circuit 5. The scan signals sequentially become a high level in one horizontal scan period (63.5 µs) or 1H period to turn on the switching elements 3 connected to the associated scan lines G 1 -G N , so that the pixels connected to the associated scan lines G 1 -G N are selectively driven one by one. A data transfer clock (horizontal clock signal) C PH and data DATA are input to the shift register 9. The data shift register 9 shifts the data DATA in response to the data transfer clock C PH and outputs the shifted data to the latch circuit 8. The latch circuit 8 latches the output from the data shift register 9 in response to a latch signal LP. The driver circuit 7 amplifies display data, latched in the latch circuit 8, supplies the amplified data to the data lines DL 1 -DL M , and charges the data lines DL 1 -DL M . The display data or signal is sent to the pixel capacitor 4 connected to one of the scan lines G 1 -G N selected then via the switching element 3 connected to that selected scan line. The above active matrix LCD panel driver section is driven at timings as illustrated in Fig. 4. As shown in Fig. 4, the drain driver 11 causes the data shift register 9 to transfer one line of data DATA in response to the data transfer clock C PH and outputs the output data of the data shift register 9 to the latch circuit 8. After temporarily latching the data in the latch circuit 8 in response to the latch signal LP, the drain driver 11 supplies the display signal via the driver circuit 7 to the active matrix LCD section. It is apparent from Fig. 4 that the conventional display driving apparatus therefore keeps transferring display data in the data shift register 9 during each scan period. With regard to relatively large characters or the like constituted by dots in units of n x m dots (n x m dots have a same data value), data for the entire display area (entire pixels of data) should therefore be supplied to the LCD section, requiring a large consumed current. Fig. 5 shows, as one example, the case of n = m = 4, i.e., each dot being quadrupled both in height and width. With the display of quadrupled height and width, the entire 16 dots in each of display units A1 to A4 each having the size of 4 x 4 = 16 dots have the same display data. For such a large character or the like, data for the entire display area (entire pixels of data) should therefore be supplied to the LCD section, increasina the consumed current. GB 2 262 377 A discloses a driving apparatus for a liquid crystal display in particular able to operate in a double-height font mode to produce enlarged images. In order to display such images this invention teaches to simultaneously supply the data of one image line to two lines of the display. In that way one line of the original image can be displayed in double height. JP-AS 147 212 discloses a matrix display device enabling an enlarged display of an image without employing digital signal processing by reading a video signal out of plural data holding means. It is the object of the present invention to provide a liquid crystal display driving apparatus which does not require the transfer of data DATA for the entire display area (entire pixels of data) even not for relatively large characters or the like constituted by dots in units of n x m dots, contributing to reducing the consumed current. To achieve the a ove object, a display driving apparatus according to a preferred embodiment of this invention comprises a matrix display panel having switching elements and data written elements, connected to the switching elements, arranged in a matrix form, for receiving data line by line and displaying an image; a data line driver circuit connected via data lines to the switching elements of the matrix display panel and having shift means for receiving data, supplied in serial, while shifting the data, and holding means for holding one line of received data, the data held in the holding means being supplied via the data lines to the matrix display panel; and control means, connected to the data line driver circuit, for inhibiting the shift means from receiving a predetermined number of lines of data after the data line driver circuit outputs one line of data. A preferred embodiment of the invention can be more fully understood from the following detailed description when referring to the accompanyed drawings, in which: Fig. 1 is a diagram illustrating the circuit structure of a display driving apparatus according to one embodiment of the present invention; Fig. 2 is a timing chart for the display driving apparatus in Fig. 1 in an intermittent drive mode; Fig. 3 is a diagram showing the circuit structure of a conventional liquid crystal display driving apparatus; Fig. 4 is a timing chart for the conventional display driving apparatus at the scanning time; and Fig. 5 is a diagram for explaining the display of quadruple height and width. Fig. 1 is a circuit diagram of a liquid crystal display (LCD) driving apparatus 20 embodying this invention, which uses the same reference numerals and symbols as used for the components of the display driving apparatus shown in Fig. 3 to denote the corresponding or identical components. Referring to Fig. 1, the LCD driving apparatus 20 has switching elements 3 and pixel capacitors 4 arranged in a matrix form at the intersections of data lines DL 1 to DL M and scan lines G 1 to G N , respectively laid out in M columns and N rows, (only one set of the switching element 3 and pixel capacitor 4 illustrated in Fig. 1). The individual scan lines G 1 -G N are connected to a scanning shift register 6 via a driver circuit 5 and the individual data lines DL 1 -DL M are connected to a data shift register 9 via a driver circuit 7 and a latch circuit 8. In this active matrix display system, pixel electrodes constituting the pixel capacitors 4 and the switching elements, for example, TFTs (Thin Film Transistors), provided one to one for the respective pixel capacitors 4, are arranged on the inner face of one electrode substrate. The switching elements 3 are driven in a matrix form so that the pixel capacitors 4 are charged via the associated switching elements 3. The driver circuit 5 and the scanning shift register 6 constitute a gate driver 10, while the driver circuit 7, the latch circuit 8 and the data shift register 9 constitute a drain driver 11. Each of the circuits constituting the gate driver 10 and the drain driver 11 is constructed by electrically connecting TFTs formed on a glass substrate 21. Each TFT 3 has a gate connected to the associated one of the scan lines G 1 -G N and a drain connected to the associated one of the data lines DL 1 -DL M . The source of each TFT 3 is connected to the associated pixel electrode constituting the associated pixel capacitor 4 whose other electrode is connected to a common line (ground). The scan lines G 1 -G N are connected via the driver circuit 5 to the individual output terminals of the scanning shift register 6 formed on the glass substrate 21. A scan shift clock signal C PV and a scan drive signal V are input to the scanning shift register 6 from a control circuit (not shown). The scanning shift register 6 sequentially sends predetermined scan signals to the respective scan lines G 1 -G N in accordance with the scan shift clock signal C PV and the scan drive signal V. The driver circuit 5, which is constituted of two stages of inverter elements connected in series, is controlled by the unillustrated control circuit. The individual data lines DL 1 -DL M are connected via the driver circuit 7 and latch circuit 8 to the data shift register 9 formed on the glass substrate 21. The data shift register 9, which has M serially-connected D flip-flops, receives a data transfer clock C PH and data DATA. The data DATA is sequentially shifted to the individual D flip-flops in the data shift register 9. A latch signal LP is input to the latch circuit 8 every time one scan line of data DATA is input to the data shift register 9. As the latch signal LP is input to the latch circuit 8, one line of data DATA is latched in the latch circuit 8. A controller 22 receives a normal mode signal M 1 or a double height/width mode signal M 2 from the unillustrated control circuit. When the normal mode signal M 1 is input to the controller 22, the controller 22 sequentially supplies one scan line of data DATA to the associated one of the scan lines G 1 -G N as per the prior art. With the enlarged mode signal M 2 input to the controller 22, however, the controller 22 stops outputting the data transfer clock C PH and the data DATA for an (n - 1) scan period after outputting one scan line of data. (The details will be given later.) Thereafter, the controller 22 outputs data DATA for the scan line G n+1 together with the data transfer clock C PH and stops outputting the data transfer clock C PH and the data DATA for the next (n - 1) scan period. Likewise, the controller 22 repeatedly outputs one scan line of data DATA and the data transfer clock C PH and stops outputting the data DATA and the data transfer clock C PH for the (n - 1) scan period until it completes the data output to all the scan lines G 1 -G N . This operation reduces the consumed power of the shift register 9. The driver circuit 7 amplifies display data, latched in the latch circuit 8, supplies the amplified data to the data lines DL 1 -DL M . The display data is supplied to the pixel capacitor 4 connected to one of the scan lines G 1 -G N selected then via the switching element 3 connected to that selected scan line. The operation of this embodiment for presenting a double height/width (intermittent drive) display will be discussed below. Fig. 2 is a timing chart for the drain driver 11 when the enlarge mode signal M 2 is supplied to the controller 22. As shown in Fig. 2, when one scan line of data DATA and the data transfer clock C PH are output from the controller 22, the latch signal LP is supplied to the latch circuit 8 so that the one scan line of data is latched in the latch circuit 8 and is also supplied via the driver circuit 7 to the data lines DL 1 -DL M . At this time, a gate signal is supplied via the scanning shift register 6 and the driver circuit 5 to the scan line G 1 , though not illustrated so that the gates of the individual switching elements 3, connected to the scan line G 1 and the data lines DL 1 -DL M , are opened, allowing the data on the data lines DL 1 -DL M to be held in the associated pixel capacitors 4. Thereafter, the controller 22 stops outputting data DATA and the data transfer clock C PH for the (n - 1) scan period, and the latch signal LP is not supplied to the latch circuit 8. In other words, the controller 22 does not output the data DATA for the scan lines G 2 -G n and the data transfer clock C PH . In the case of the quadruple height/width display as exemplified in Fig. 5, after the controller 22 outputs the data DATA for the scan line G 1 and the data transfer clock C PH , it stops outputting the data DATA and the data transfer clock C PH for the scan lines G 2 -G 4 . During this period, the data DATA for the scan line G 1 is latched in the latch circuit 8 and is supplied via the driver circuit 7 to the individual data lines DL 1 -DL M , so that the data DATA for the scan line G 1 is accumulated in the pixel capacitors 4 connected to the individual scan lines G 2 -G 4 . In the case shown in Fig. 5, the same data for the scan line G 1 is supplied to the scan lines G 2 -G 4 and is held there. Then, the data DATA for the scan line G n+1 and the data transfer clock C PH are output from the controller 22, and are supplied via the data shift register 9 and the latch circuit 8 to the data lines DL 1 -DL M . This data DATA is held in the pixel capacitor 4 connected to the scan line G n+1 . During the next (n - 1) scan period too, the outputting of the data DATA and the data transfer clock C PH from the controller 22 is inhibited and the data for the scan line G n+1 , latched in the latch circuit 8, is held in the pixel capacitors 4 connected to the scan lines G n+1 -G 2n . In the example of Fig. 5, the same data for the scan line G 5 is supplied to the scan lines G 6 -G 8 and is held there. In the subsequent operation, as already discussed above, the controller 22 repeatedly outputs one scan line of data DATA and the data transfer clock C PH and stops outputting the data DATA and the data transfer clock C PH for the (n - 1) scan period, so that for the entire scan lines G 1 -G N , data is held in the pixel capacitors 4 connected to the individual scan lines. According to the display driving apparatus embodying this invention, as described above, the number of operations of the data shift register 9 and the latch circuit 8 becomes 1/n of the conventional case, thereby reducing the consumed power accordingly. Although this embodiment has been described with reference to an enlarged display as one example, the present invention may be widely adapted for a display driving apparatus which presents the same display on a plurality of scan lines such as a time display. In this case, the numbers of scan lines for the same display need not all be the same. Although this embodiment switches between the normal driving that causes the controller to output data and the data transfer clock to all the scan lines and the intermittent driving that stops outputting data and the data transfer clock to predetermined scan lines, this invention may be applied to an apparatus which does not execute such switching.

Claims: A display driving apparatus comprising: display means (3,4) for displaying an image of a plurality of lines arranged in a predetermined direction; control means (22) for controlling data to be displayed on the plurality of lines on the display means (3,4); a data line driver circuit (11) including a data shift register (9) for receiving data externally supplied in serial by the control means (22) while sequentially shifting the data, and a latching means (7,8) for receiving the data from the data shift register (9), for latching them line by line and for supplying them to the plurality of the lines on the display means (3,4); and a scan line driver circuit (5, 6 and 10) for sequentially supplying a scan signal to each of the plurality of lines on the display means (3,4), characterized in that the control means (22) supplies data only for a first of n successive lines for displaying identical images on the display means (3,4) to the data shift register (9) of the data line driver circuit (11) in order to enable output of the data via the latching means (7,8) to the display means (3,4), whereas the control means (22) inhibits to supply data for the subsequent (n-1) identical lines to the data shift register (9), such that the data for the first of the n identical lines is read out from the latching means (7,8) (n-1) times in order to be sequentially output to the display means (3,4). The display driving apparatus according to claim 1. characterized in that the display means (3,4) is a liquid crystal display panel. The display driving apparatus according to claim 1 or 2, characterized in that the display means (3,4) comprises switching elements (3) and data holding elements (4) connected to the switching elements arranged in matrix form. The display driving apparatus according to claim 2, characterized in that the switching elements (3) are constituted of thin film transistors. The display driving apparatus according to claim 3 or 4, characterized in that the data holding elements (4) are constituted of capacitor elements. The display driving apparatus according to any one of claims 1 to 5, characterized in that the display means (3,4) includes a substrate (21), and the data line driver circuit (11) is formed on the substrate (21). The display driving apparatus according to one of claims 1 to 6, characterized in that the data line driver circuit (11) is constituted of thin film transistors. The display driving apparatus according to one of claims 1 to 7, characterized in that the scan line driver circuit (5, 6 and 10) for sequentially accessing the switching elements (3) line by line regardless of supply of data to the data shift register (9) or inhibition of data supply thereto. The display driving apparatus according to one of the claims 1 to 8, characterized in that the scan line driver circuit (5, 6 and 10) is constituted of thin film transistors. The display driving apparatus according to one of claims 1 to 9, characterized in that the control means (22) has means for switching between a normal driving mode in which the data line driver circuit (11) supplies one line of data to the display means (3,4) whenever receiving one line of data from the control means (22) and an intermittent driving mode in which the control means (22) stops outputting data to the data shift register (9) for a predetermined number of lines after the data line driver circuit (11) has supplied one line of data to the display means (3,4). The display driving apparatus according to one of claims 1 to 10, characterized in that the latching means (7,8) comprises a latch circuit (8) for receiving the data from the data shift register (9) and for latching them and a driver circuit (7) for amplifying the data to be displayed after they have been read out from the latching circuit (8) and before they are supplied to the display means (3,4).

Inventors: KANBARA MINORU C O CASIO COMPU, KANBARA, MINORU, KANBARA, MINORU, C/O CASIO COMPUTER CO., LTD.
Applicants: CASIO COMPUTER CO LTD, CASIO COMPUTER CO., LTD.
Application year: 1994
Main classification: G09G3
IPC codes: G09G3, G02F1